Knee
ACL Tear
전방십자인대 파열
Complete rupture of the primary knee stabilizer causing instability and hemarthrosis
- How common
- Very Common Sports Injury
- Typical age
- Athletes aged 15–40
What is it?
Non-contact pivoting/hyperextension tears the ACL (usually at femoral attachment). Women are 2–8x more susceptible. Rich vascularity causes immediate hemarthrosis.
Commonly affected: Femoral attachment most commonly torn; intraligamentous tears less common
How it develops
- Non-contact Rotational ForceLanding or pivoting: tibia translates anteriorly on femur under valgus stress
- ACL Rupture (audible pop)Ligament tears — patient hears/feels a pop; immediate instability
- Immediate HemarthrosisLigament vascularity causes hemarthrosis within 1–2 hours of injury
- Knee InstabilityLoss of anterior tibial restraint; giving way with pivoting activities
Symptoms
- Rapid HemarthrosisKnee rapidly swells within 1–2 hours — distinguishes from meniscal tear
- Audible Pop + Giving WayPathognomonic 'pop' sound and immediate giving way sensation
- InstabilityKnee gives way with pivoting, cutting, and decelerating — anterior tibial subluxation
- Inability to Weight BearImmediate inability to continue play; difficulty weight-bearing
- Chronic Instability (if untreated)Chronic ACL deficiency → secondary meniscal and cartilage damage
How it is examined
- Positive Lachman Test (85% sensitive)Knee 20–30° flexion: anterior tibial displacement with soft endpoint = positive (most sensitive test)
- Anterior Drawer TestKnee 90° flexion: anterior tibial drawer positive (less sensitive than Lachman)
- Positive Pivot Shift TestMost specific test — tibial subluxation/reduction confirms rotational instability
Imaging
X-ray does not show ligament tears. Segond fracture (lateral capsule avulsion) is pathognomonic for ACL injury.
- Usually normal or joint effusion
- Segond fracture (lateral tibial rim avulsion — pathognomonic)
- Cannot see bone contusion (need MRI)
MRI confirms ACL tear and evaluates concurrent injuries (meniscus 50%, bone bruise, cartilage, PCL, collaterals).
- Loss of ACL continuity (T2 high signal)
- Bone bruise: lateral femoral condyle + posterolateral tibia (kissing contusions)
- Concurrent meniscal tear (50%)
- Evaluate PCL/collaterals
Non-surgical care
- Acute RICE + RehabilitationAcute: RICE + aspiration of hemarthrosis; rehab to regain quad strength and ROM
Conservative options are generally tried first. Medications listed here can have side effects — discuss them with your prescriber.
When surgery is considered
Athletes wishing to return to sports, young active patients, combined injuries
Procedures that may be discussed
- Autograft: BTB (bone-tendon-bone patellar) or hamstring (gold standard)
- Allograft: cadaveric graft
- Pre-operative prehab 4–6 weeks improves outcomes
Outlook
Return to sport at 9–12 months post-op. 85–90% return to pre-injury level; reinjury rate 15–25% in young athletes.